As a method of growing a semiconductor single crystal such as the III-V group compound semiconductor single crystal including GaAs, GaP, GaSb, InP, InAs, and InSb as well as the II-VI group compound semiconductor single crystal including CdTe, CdMnTe, CdZnTe, HgCdTe, ZnSe, ZnSSe and the like, various growing methods have been conventionally proposed.
Typical methods of growing a semiconductor single crystal include the Czochralski method, horizontal Bridgman method, as well as the vertical boat method such as the vertical Bridgman method (VB method) and vertical gradient freeze method (VGF method). Such methods of growing semiconductor single crystals include the steps of placing seed crystal and raw material melt in a crucible, and solidifying the raw material melt from the seed crystal side to grow a semiconductor single crystal.
In order to prevent the escape of the V group and VI group that are volatile components from the growing semiconductor single crystal in the aforementioned methods of producing a semiconductor single crystal, a sealant is generally employed. For a sealant, boron oxide (B2O3) is well known, as described in Patent Literature 1 (Japanese Patent Laying-Open No. 6-219900), for example. However, in the case where B2O3 is used as a sealant when a doped type semiconductor single crystal such as semiconductor single crystal including silicon (Si) as a dopant is to be grown, B2O3 will capture Si, leading to the disadvantage that the Si concentration in the semiconductor single crystal will not be uniform. Furthermore, the usage of B2O3 as a sealant has the tendency of generating scum such as of boron arsenic (B13As2) due to the reduction of B2O3 to Si. In this case, the generated scum will adhere to the growing semiconductor single crystal. As a result, the produced crystal had a defect such as twinning and polycrystallization.
In view of such defects, Patent Literature 2 (Japanese Patent Laying-Open No. 3-57079) and Patent Literature 3 (Japanese Patent Laying-Open No. 8-151290), for example, propose the approach of using B2O3 including silicon dioxide (SiO2) (hereinafter, referred to as “SiO2— B2O3”) as the sealant. The usage of SiO2—B2O3 as a sealant can suppress the capture of Si and generation of scum.
SiO2—B2O3 is also known to effectively prevent the wetting between the crucible and the raw material melt by coating the inner surface of the crucible, in addition to its function as a sealant. By preventing the wetting between the crucible and the raw material melt, the defect such as twinning and polycrystallization can be prevented effectively. For example, Patent Literature 4 (Japanese Patent Laying-Open No. 8-133882) discloses the method of forming an SiO2—B2O3 film on the inner wall of a crucible made of pyrolytic boron nitride (PBN) using the so-called sol-gel method.